Rhinoviruses are a major cause of upper respiratory tract disease throughou life. Currently there are over 100 serotypes identified. Rhinoviruses hav been grouped according to their ability to bind to specific cell surface proteins and are classified as belonging to either a major (I-CAM1 binding) or minor receptor binding group; in addition, RVs can be grouped according to susceptibility to antiviral compounds. Previous work in this laboratory using polyclonal monospecific antisera has confirmed that antisera of viruses belonging to the same receptor binding group, in general, are strongly reactive with VP1 of a prototypic strain of rhinovirus, (RV), in western blot assays suggesting that these viruses also share linear epitope in addition to the tertiary structures that define receptor binding properties. For example, 9 of 10 antisera from viruses belonging to the minor B receptor group react with the prototypic strain, rhinovirus type 2, in western blot assay; however, antisera to rhinovirus type 31 did not reac with type 2 proteins. In order to investigate the relationships among VP1 o rhinoviruses belonging to the minor B receptor group we derived viral RNA from plaque purified RV type 31 and amplified the VP1 sequence by polymeras chain reaction for direct sequencing. The deduced amino acid sequence for RV type 31 has been determined and compared to all other published RV VP1 sequences; interestingly, the VP1 of all rhinoviruses are highly conserved at the amino acid level; conserved regions are predominantly in the inner one third of the protein with divergence from the consensus sequence locate primarily at the amino and carboxy termini. This work serves as a basis fo exploring evolutionary relationships among human picornaviruses and in the future could serve as a technique for rapidly discriminating RV strains prior to initiating antiviral therapy.